1. Field of the Invention
The present invention relates to a radioisotope proximity sensor. More particularly, the present invention relates to a radioisotope proximity sensor for use in an electromechanical actuator.
2. Description of the Prior Art
Measurement of displacement and/or velocity of a moving armature in relation to a stationary structure near the armature is desirous for the purpose of electronic control in a valve timing system. For example, for a moving armature it is important to maximize soft-landing control. To such an end it is desirable to ensure that the armature comes in at the lowest velocity possible. In particular, it is desired for an E-core of an electromagnetic actuator of which the armature is a functioning component.
Other sensing techniques that have been explored include those that sense magnetic fields, e.g. Hall-effect, eddy-current, variable reluctance (VR), gigantic magneto-restrictive (GMR), direct inductance change of driving current, linear variable displacement transformer (LVDT) sensors, those that sense visible or infrared light, e.g. photosemiconductor source/detectors, backscatter, Doppler, interrupted beam, and those that sense electrostatic fields such as capacitive proximity or velocity sensors.
The disadvantages of each of the foregoing sensors are unique to their individual sensing techniques. The magnetic sensors have their signals corrupted by being immersed in a changing magnetic field that is a normal function of the electromagnetic actuator. Magnetic sensors have improved performance when operated at a distance from the actuator's magnetic circuit, but such a configuration increases the overall dimensions of the actuator. Optical sensors have the disadvantage of environmental sensitivity to contaminations that obscure or absorb the light, such as oil, dirt or suspended particles. Fiberoptic techniques are an option to accommodate optical methods, but are costly and may not be robust. Capacitive sensors are sensitive to electrostatic noise impressed on their unshielded exposed sensing plates. Such electrostatic noise is also present during actuator operation.